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Food allergy

A food allergy is when your body's immune system reacts to particular foods, for example eggs or nuts, which it sees as harmful. Most food allergy reactions are mild, but sometimes they can be life-threatening and even fatal.

If you have an allergy, it means that your body's immune system reacts to a substance called an allergen. Allergens aren't usually harmful and most people aren't sensitive to them.

An allergic reaction happens after your immune system mistakes an allergen, for example nuts, for a harmful invader and produces antibodies. The first time you eat or touch the specific food your body doesn’t react, and you don’t have symptoms. This is called sensitisation. However, the next time you eat or touch the food, your antibodies are ready to react with it. This causes your body to release chemicals, which leads to a range of symptoms called an allergic reaction.

Food allergies in young children are more common than in adults, but many children grow out of allergies as they get older. You can develop a food allergy as an adult, even if you never had allergies as a child. In the UK, about one to two in 100 people have a food allergy.

If you have hay fever or an allergy to latex, you may also find that you’re allergic to certain foods. This is called cross-reactivity.

A food allergy is sometimes confused with food intolerance or food poisoning. These can make you feel ill but they aren't usually harmful in the same way that a true food allergy can be.

Details

The symptoms you get during an allergic reaction depend on where in your body chemicals are being released, and how severe your allergy is. If you have a very severe reaction, called an anaphylactic reaction, your whole body may be affected.

Your symptoms will usually develop within a few minutes of eating or touching the food that causes your allergic reaction. However, some food allergy symptoms can take a few hours to develop. The main symptoms may include:

These symptoms may be caused by problems other than food allergy. If you think you may have a food allergy, see your GP for advice. If you have a severe reaction or have trouble breathing, you may need to seek urgent medical attention.

If you're severely allergic to a food, then you can have an allergic reaction by just touching or being near the food, or by being near someone who is eating it.

Your GP will ask about your symptoms and examine you. He or she will ask you questions about your allergic reaction including how quickly it develops, how severe it is and what you think may have caused it.

If your GP thinks you may have a food allergy, he or she may carry out a skin prick or radioallergosorbent (RAST) test, or refer you to a specialist allergy clinic for tests. Common allergy tests are listed below.

Skin prick tests. A small and diluted amount of the possible food allergen is put on your skin and a very small, fine scratch is made through it. If your skin becomes red and swollen around the scratch, your test is positive for that particular food.

Blood tests. These are called RAST tests and can measure the amount of antibodies in your blood to a suspected food allergen. You may have a blood test if you can’t have a skin prick test for some reason, for example, if you have severe eczema.

Elimination diets. This is when you stop eating the food or foods that may be causing your allergic reaction to see whether your symptoms get better. If they do, you then start eating the suspected food again to see if your symptoms come back. If they do, it’s likely that you’re allergic to that food.

Food challenges. If you have a severe food allergy, you will be given a small amount of the food which may be causing your allergic reaction, to see what happens. You should only have this type of test done in a hospital or clinic, where you can be treated quickly if you do have a severe reaction.

There are many other tests available for food allergies, such as applied Kinesiology, hair analysis and Vega testing, but none of these has been shown to be effective at testing for food allergy.

Most allergic reactions won’t require emergency treatment. However, if you have a severe food allergy and have an anaphylactic reaction to it, you can give yourself an injection of adrenaline as soon as your symptoms start. Adrenaline is a hormone (a chemical that occurs naturally in your body) that relaxes your muscles and helps to reduce any swelling, which makes it easier to breathe. It works very quickly and starts treating your reaction straight away.

Your doctor can prescribe a single dose of adrenaline in the form of a pen. This is a pre-loaded syringe containing adrenaline that you can inject yourself. Once you have injected the adrenaline, or someone has done it for you, you should call an ambulance and get further medical help immediately. Although adrenaline works very quickly, it doesn’t work for very long and you’re likely to need more treatment.

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The exact reasons why some people have food allergies and others don’t aren't fully understood.

Most people with a food allergy have a type called an IgE-mediated allergy. This usually happens within a few minutes of eating or touching a specific food. The reason why this happens isn’t yet known. However, experts think that a number of things together may cause this type of allergic reaction, such as your genes and the environment you live in.

The second type of food allergy is known as a non-IgE-mediated food allergy and develops because of cell reactions in your immune system. It happens several hours or days after you have eaten the food and your symptoms, such as eczema and diarrhoea, usually last longer than symptoms from an IgE-mediated reaction.

If you have other allergies or conditions, such as eczema or asthma, you may be more likely to develop a food allergy. This is called atopy. If someone else in your immediate family has these conditions, for example your parents, you’re more likely to have an allergy, although it may not be to the same thing.

The main complication of food allergies is anaphylaxis. This is a severe, full-body allergic reaction which can be life-threatening. If you have an anaphylactic reaction to a food, you may have breathing problems, your airways can swell and you can quickly collapse and become unconscious. If you think someone is having an anaphylactic reaction, call for emergency help. Food allergies are more likely to trigger an anaphylactic reaction in children than adults. However, this type of reaction is rare, with less than one in 1,000 people having an anaphylactic reaction at some time in their lives.

Many children grow out of food allergies, such as cow’s milk, eggs and wheat allergies, as they get older. Around two in 10 children outgrow an allergy to peanuts.

Most food allergy reactions are mild, though they can be uncomfortable and distressing.

There isn't a cure for food allergy. However, you can prevent a reaction by not eating the food that you're allergic to. If you do eat or come into contact with the food that causes a reaction, you can treat the symptoms yourself.

You can buy antihistamines at your pharmacy without a prescription. These medicines help to dampen down your body’s response to an allergen and can help to ease your symptoms. Some antihistamines can make you feel drowsy. Always read the patient information leaflet that comes with your medicine and if you have any questions, ask your pharmacist for advice.

If you have a severe food allergy, ask your GP or allergy specialist to refer you to a dietitian. Your dietitian can show you how to identify problem foods and how to make sure you have a healthy, well-balanced diet without them.

If you have a food allergy, it makes sense to try and not eat the food or foods that cause you to react. The following tips may help.

Check the labels on foods carefully, to find out if they contain what you're allergic to. There are laws that food manufacturers have to work to that mean that all pre-packed food sold in the UK and the European Union must say on the label whether it contains an allergen, such as eggs or nuts.

Take extra care when you’re cooking at home, to make sure you don’t contaminate your food with any foods that you’re allergic to. This may mean keeping certain foods, utensils and chopping boards separate and always clean utensils, chopping boards and surfaces directly after use.

When you’re eating out, read menus carefully and tell staff about your food allergy. Take extra care where foods can be easily contaminated, such as buffets and parties.

Take care when you’re buying foods that aren’t pre-packed, for example foods that you might buy from sandwich shops, deli counters or bakeries. These foods won't have detailed ingredients and allergy labelling, and may also be contaminated by other foods.

Can I have the flu and yellow fever vaccines if I am allergic to eggs?

Answer

Both the flu vaccine and the yellow fever vaccine are prepared using egg protein. If you have an egg allergy, you should get advice from your allergy specialist before having either vaccination.

Explanation

The flu vaccine is prepared using eggs, so there may be small amounts of egg protein in it. If you have a severe allergy to egg, the flu vaccine may cause an anaphylactic or severe reaction. Therefore, you should get advice from your allergy specialist or your GP about having the vaccination.

If you have been allergic to egg in the past, but are able to eat egg now, then you should be able to have the flu vaccine.

The vaccine for yellow fever does contain egg protein. Therefore, if you need the vaccine because you’re travelling abroad, you should get advice from your allergy specialist before having the vaccine.

How can I prevent my child from developing food allergies and will they grow out of them?

Answer

There are no proven ways to predict whether your child will have food allergies or to prevent your child from developing them. Many children do grow out of food allergies by the time they become teenagers, although this is less likely to happen if your child has a peanut allergy.

Explanation

Some women consider changing their diet during pregnancy or when breastfeeding to try and prevent a food allergy affecting their child. However, there is no research which shows that doing this will prevent your child developing a food allergy.

Doctors currently recommend that when you’re pregnant and breastfeeding you should eat a healthy, balanced diet. You don’t need to cut out any particular foods, including peanuts, unless you have an allergy to them yourself.

There is very little research to show that breastfeeding your baby can help to prevent food or other allergies from developing. However, breastfeeding has many other benefits for both you and your baby.

Most children grow out of milk, egg, wheat and soya allergies by the time they become teenagers. However, if your child has a tree nut or peanut allergy, he or she is less likely to grow out of it. How long it takes for your child to grow out of an allergy depends on how severe their allergic reaction to it is, and what food is causing the reaction.

I ate shellfish at a restaurant last night and have been sick and have a rash on my skin – is this a food allergy?

Answer

Food allergy and food poisoning can often have very similar symptoms, so it can be difficult to know which of these conditions is causing your symptoms. If you’re concerned speak to your GP.

Explanation

Diarrhoea, feeling sick, vomiting and gastrointestinal discomfort can all be symptoms of both food allergy and food poisoning. However, there are some symptoms which you may get in food poisoning but not in food allergy and vice versa.

The common symptoms of food poisoning include diarrhoea, feeling sick, vomiting, abdominal (tummy) cramps, and sometimes a fever.

The common symptoms of food allergy are also diarrhoea, feeling sick, vomiting and bloating. However, you may also have symptoms such as coughing and wheezing, a runny nose, tingling or swollen lips, mouth, tongue and throat and skin reactions, such as a rash or hives.

These symptoms may also be caused by problems other than food allergy or food poisoning. If you’re worried about whether you have a food allergy, food poisoning or another condition, see your GP.

If I have a severe peanut allergy, am I at risk of a reaction if I travel by plane?

Answer

People with food allergies travel by air every day without any problems, and it’s unlikely that you will have a reaction. However, if you have a severe peanut allergy it’s sensible to take extra care with your food and to let your airline know about your allergy. Alternatively take your own food onboard with you.

Explanation

Some people with a peanut allergy have found that when they travel by aeroplane they sometime have an allergic reaction during the flight. This may be because of the snacks that are served. When packs of peanuts are opened, the dust spreads around the cabin. This can cause an allergic reaction in people with a severe peanut allergy. However, this reaction is usually mild. The meals that are served on aeroplanes may also contain, or be contaminated with, peanuts.

If you have a severe peanut allergy and are concerned about having a reaction on a flight there are a number of things you can do. The main ones are listed below.

When you book your ticket tell the airline that you have a severe peanut allergy and ask for a special meal prepared without peanuts or contamination with them. You should check that this has been arranged when you check in and when you get on the plane. The best way to make sure your food is completely free of nuts and nut traces is to take your own with you.

Some airlines don’t serve peanut snacks, and some will remove them from a flight if you contact them well in advance. Ask your airline if they would consider this.

Tell the cabin staff that you have a severe peanut allergy when you get on your flight.

If you have a very severe peanut allergy, always make sure you have your medicines with you and speak to your allergy specialist before travelling by plane.

I have a peanut allergy and I've heard I may be at risk of having an allergic reaction caused by lupins. Is this true?

Answer

Yes, if you have a peanut allergy, you can also react to lupins or products that contain lupin flour or seeds. This is because lupins contain many of the same allergens as peanuts.

Explanation

Lupins are a type of flower and they are related to peanuts. This means that they may cause you to have an allergic reaction if you’re allergic to peanuts. Lupin seeds can be ground to produce flour or they may also be used as an ingredient in foods like seeded bread. Lupin flour isn’t used very often in foods made in the UK. It’s more commonly found in foods that come from Europe, such as pastries and pasta. People can have severe reactions to lupin. So, if you’re allergic to peanuts it’s important to check food labels for lupin and to take extra care if you’re eating foods from Europe.

By law, all pre-packed food produced in the UK and the European Union must say on the label if it contains lupin.

Is it safe for me to eat or use products containing peanut oil if I have a peanut allergy?

Answer

This depends on whether the oil is refined or unrefined. If you have a peanut allergy, you're unlikely to have an allergic reaction to refined peanut oil, and if you do it will probably be mild. However, you may be more likely to have a reaction to unrefined peanut oil.

Explanation

Research has shown that if you have a peanut allergy, you're very unlikely to have a reaction to refined peanut oil. The allergic part of peanuts is the protein. However, peanut oil contains fat, not protein. Refined peanut oil has been shown to be very low risk and you’re very unlikely to have a reaction to it. If you do react, the reaction is likely to be mild. Unrefined peanut oil may still contain small amounts of peanut protein. This means you may be more likely to have an allergic reaction to it.

Peanut oil is listed as ‘peanut oil’ on food labels, however the label won’t say whether this is refined or unrefined oil. Peanut oil is also sometimes called groundnut oil.

Some emollients and skin creams contain arachis oil, which is peanut oil. Although you’re unlikely to have a reaction to these products, if you have a very severe reaction to peanuts, it makes sense to not use products that contain arachis oil.

My daughter is allergic to eggs – is it safe for her to have the measles, mumps and rubella (MMR) vaccine?

Answer

Yes, it's fine for your daughter to have the MMR vaccine if she has an allergy to egg.

Explanation

There has been concern among some parents about giving the MMR vaccination to a child with an egg allergy. This is because it was thought that the measles part of the vaccine was produced using cells from eggs. However, the measles part of the MMR vaccine is produced by growing it on cells from hens, not eggs, so it has no egg in it at all. Therefore, it’s safe for your child to have the MMR vaccination.

Anaphylaxis: assessment to confirm an anaphylactic episode and the decision to refer after emergency treatment for a suspected anaphylactic episode. National Institute for Health and Clinical Excellence (NICE), December 2011. www.nice.org.uk

About allergy. Allergy UK. www.allergyuk.org, published March 2012

Food allergy and intolerance testing. British Dietetic Association. www.bda.uk.com, published January 2012

Types of allergy. Allergy UK. www.allergyuk.org, published March 2012

Guidelines for the diagnosis and management of food allergy in the United States: report of the NIAID-Sponsored expert panel. National Institute of Allergy and Infectious Diseases (NIAID), December 2010. www.elsevierhealth.com

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